Safety motor fuel



atented Aug. 24, 1943 SAFETY MOTOR FUEL Walter A. Herbst, Union, N. J., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 31, 1940,

Serial No. 372,569

16 Claims.

tane safety fuels for aviation engines has presented some important problems with regard to avoidance of fire hazards.

The use of high flash point naphthasfor reducing fire hazard is well known in cleaning, paint, and other industries which make use of solvents. -Hitherto, it has been presumed that solventslike kerosene or Stoddard's solvent, and the like, with a minimum flash point of 105 F.,

have adequate safety from fire hazards, and accordingly, without further investigation, this same minimum flash point was generally regarded as an index of safety for motor fuels. By recent investigations applied particularly to motor 'fuels for aviation service, I have found that the tests for safety of these aviation fuels depend upon factors not present in the use of solvents and that, moreover, other significant characteristics of fuels must be taken into account, which makes the problem with respect to fuels quite distinctive.

The main object of the present'invention-is to control the explosiveness and inflammability of motor fuels with the least possible detraction from their desired volatility characteristics.

To accomplish the objects of the present invention it was determined by a number of special tests, what service conditions created a fire hazard in the use of the fuels and to what extent the fuels have to be modified with respect to their tendencies to flash, burn, and explode, so as to reduce these tendencies to a minimum, Further, in carrying out these tests, it was determined that the potential fire hazards are greatly reduced with less impairment of the volatility characteristics of the fuel by adding to the fuel proper amounts of selected noble sub More stances, more particularly, certain highly volatile organic halides.

Contrary to the long accepted belief that merely a removal of highly volatile fuel components to increase the minimum flash point of a fuel to about F., or thereabove, insures the safety of the fuel against fire hazard, I have found thatwhen the fuel becomes subjected to a variation of conditionszbrought about by change in altitude it becomes unsafe. As a matter of fact, the more volatile fuels, with flash points below 105% F. are less prone to form explosive mixtures in fuel-tanks at certain high altitudes than are the commonly regarded safety fuels with flash points of about 105 F. or thereabove, which actually can form explosive mixtures under practical aviation service conditions. Thus, at high altitudes, the variable combinations of temperature and pressure imposed on a fuel in a supply tank have certain changing effects on the air to vapor ratio in the fuel tank. For instance, at atmospheric pressure of sea level, the flre hazard may be negligible for the ordinary safety fuel having a flash point of 105? F., but as the pressure is reduced by gaining of altitude, the temperature at which the fuel is subject to explosion drops sharply. At an altitude of 25,000 feet the ordinary safety fuel forms an explosive mixture in the tank at 68 F.

Another important property of a fuel, previously overlooked in evaluating safety characteristics of fuels, is the fire point and rate of buming. Those should be taken into account to decrease the danger from conflagration caused by a spark, open flame, or a hot metal surface in the. case of a plane crash. Thus, in evaluating the safety factor of fuels, it was found necessary to make determinations on inflammability limits, spontaneous ignition temperatures, and burning characteristics.

From a long series of tests with variations of all practical factors, it was ascertained that an aviation fuel having a minimum flash point 'of 124 F. more properly obviates potential explosive hazards 'under all practical combinations of fuel temperature and altitude pressures. This determination took into' consideration the initial fuel temperature, the. rate of-change in altitude, the rate of cooling, the degrees of agitation at the vapor-liquid interface in a fuel supplytank, and

was determined up to the altitude of 30,000 feet at 30 0. However, such a requirement seriously limits the availability of high octane number hydrocarbon fuels on account of manufacturing compounds and indicate that to raise the flash point of an ordinary petroleum naphtha through limitations and requires a fuel of such low vola- 5 the margin of flash point safety so that the fuel tility that difiiculties in starting and engine operahas a flash point well above the minimum of tion may be encountered due to improper car- 124 F. without sacrificing volatility, not all nonburetting and the lack of a proper air to fuel inflammable compounds can be satisfactorily ratio in the fuel induction system of the engine. employed. For example, ethyl iodide, normal It will be appreciated by those skilled in the art propyl iodide, and carbon tetrabromide are subthat the hydrocarbon fuels differ in their propenstantially ineffectual for raising flash point of the sities for forming vapors at different temperafuel. This same relationship of boiling point to tures. For example, an aromatic fuel withaflash effectiveness of the non-inflammable agent has point of 102 F. in the range of altitude from been found to hold in all other instances includsea level to 2 ,000 feet forms a mixture which is ing that of carbon tetrachloride (boiling point too lean to burn in a fuel tank at C., from 76.8 C.), which is known to have been used in 25,000 feet to 57,000 feet, it forms an explosive hydrocarbon solvents for decreasing fire hazards, mixture, and above 57,000 feet forms a mixture but which is not suitable in aviation safety fuels. which is too rich to burn. Further observations prove that excessive con- To determine whether and how a noninflam- 20 centrations of any completely noninflammable mable addition agent could be satisfactorily used compounds are necessary to effect an appreciableto prevent the formation of an inflammable mixincrease in the flash point of ordinary motor ture in fuel tanks through a wide range of altifuels. In general, the less highly chlorinated tudes without impairing the volatility charactercompounds are not sufficiently non-inflammable istics of the fuels, a number of determinations and are required in excessive concentrations for were made on different types of aviation fuels with any practical effect on increasing the flash point. varying amounts of the addition agents. But, high concentrations of the halogenated A hydrocarbon aviation fuel principally comcompounds are undesirable in the motor fuels, posed of hydrogenated tri-isobutylene, having a for they tend to give corrosion troubles and to flash point of 104 F., was blended with 1 or 2% of decrease the lead susceptibility of the fuel in promethyl iodide, and no inflammable mixtures were portion to their concentration. Hence, it was formed at any reduced pressure for a temperature found advisable to find the optimum types and of 25 C. With 0.5% of methyl iodide added to concentrations of the agents and the most satisthe same type of hydrocarbon fuel, inflammation factory type of fuels to be blended in forming was obtained over a narrow range of pressure at practical aviation safety fuels. 24 C. The highest absolute pressure at which In determining what types of hydrocarbon inflammation was obtained was 238 mm. of merb s fuels Could e P p y u t Optimum cury, corresponding to a minimum altitude of and minimum proportions of the noninflamma- 29,200 feet. ble compounds, various naphthas were blended The important advantage of the noninfiam- 49 with the noninflammable agents and in varying mable addition agents is made apparent in tests proportions. It was determined from these tests of these agents added to naphthas lacking in the that about 0.5% by volume is the minimum of desired degree of safety. A valuable benefit of any suitable noninflammable agent which could these addition agents is to make it permissible to F be used to obtain a satisfactory elevation in the use naphtha fractions of more desirable volatility flash point of the fuels and that it was unnecesand to greatly increase the availability of hydrosary to use amounts as high as 5% of the agent, carbon fuel bases for use in safety fuels which so that the preferred concentration of the nonwere otherwise excluded, inflammable agent of proper characteristics is in It is indicated by the following data that the 50 the range of 1% to about 2%. This concentravolatility of the addition agent significantly govtion factor is illustrated in the following table erns the ability of the agent to raise the flash with respect to a hydrogenated tri-isobutylene point of the fuel blend to a safe minimum point. fuel and an aromatic safety fuel, which mark the The indications from data of this kind are that two extremes in types of hydrocarbon bases. only those compounds having boiling points below 0. are actually effective for accomplish- TABLE II ing the purpose of this invention.

Boiling TABLE I Closed cup 3:35: Efiect of non-inflammable compounds on the 60 F lg flammable flash point of a na/phtha g Boiling point of Hydrogenated tri-isobutylene safety fuel" 104 Closed noninflammable Ditto+2% methyl iodide 175 42. 5 cup flash ompo nd gi: +5%methy li giidp 175 42.5 ioliifgzfimrif.f:::::: :t it? c. F. Ditto+5 vol. per cent methyl iodid 175 "lift Dltto+1 vol. per cent methyl iodide 111 42. 5

. Petroleum naphtha "Ii 102 I v gtfi fiffyfiff gEff 23.7 74.1 7 Toillustrate how the hydrocarbon fuel base $23123: ticillf tmar must also correspond to a certain standard in orethane 15; 13.1 der to make the use of the noninflammable agent gmgiggz 2 3 Maj: 102 5 practically effective, data are presented in the mm+s% carbon tetrabromidcn 102 189 312. 2 following table on the eifects of the agent in fuel bases of varying volatility and flash point:

' mide.

1 Pensky-Martin flash 240 F.

From data such as that presented in Table 111, it was found that it is important to have the initial boiling point of the hydrocarbon base stock substantially at a minimum of approximately 275 F. with the specific agent methyl iodide. However, the minimum boiling point, and similarly the minimum flash point, of the hydrocarbon base fuel can be varied with the boiling point of the selected noninflammable agent employed. This has been very clearly demonstrated. For example, methyl bromide which is more volatile than methyl iodide and has a boiling point of about 45 C. (40 F.) can be blended in small amounts witha hydrocarbon base stock having a flash point as low as from 15 to F. (about 20 F.) to obtain true safety fuels having closed-cup tester flash points well above 124 F.

From investigations of the relationship between the boiling point of the noninflammable agent and the flash points of the hydrocarbon base stocks, and the blends, the conclusion was reached that the minimum flash point of the hydrocarbon base fuel should be limited, in that the boiling point of the noninflammable agent should be no more than about Fahrenheit degrees above the flash point of the base fuel. and preferably this difference should be less than 20 F.

The relationship between the flash points and boiling points of the fuels and the blends are rather peculiar. As a rule, the flash point of the conventional petroleum distillate fuels varies directly in proportion to the initial boiling point of the fuel, and can be estimated approximately by use of the following formula:

Closed-cup flash point (F.)

0.73 initial boiling point (F.) -122 In contradistinction to this relationship, with the blended noninflammable agents having boiling points below 60 C. (140 F.), the flash points of the blends decrease with the boilin'gpoint of the agent quite markedly, this decrease amounting substantially to the difference between the boiling points of the agents employed; This is illustrated, for example, in the difference between methyl iodide and the lower boiling methyl bro- The methyl bromide, boiling at 40 F., boils about 68 Fahrenheit degrees below the boiling point of the methyl iodide, and accordingly the hydrocarbon base fuel blended with methyl bromide can have a flash point about 68 Fahrenheit degrees below the flash point of the hydrocarbon base stock blended with the methyl iodide to form a blend of comparable high flash point above 124 F.

In general, the hydrocarbon base stock to be used with any of the inflarmnability controlling agents should boil substantially within the gasoline boiling range;

1, e., should have volatility boiling point no lower than about 100 F. and an end point ordinarily less than 437 F.

Unless otherwise indicated, the flash point referred to is that determined with a tag closed tester (A. S. T. M. standard method).

By noninflammable compounds are meant those having substantially no explosive limits with air and which have flash points considerably above 175 F. I 7

Due to the numerous factors involved in formulating aviation safety fuel safeguarded from all potential hazards in aviation service with a minimum lowering of volatility and with a minimum concentration of the noninflammable agent, it is somewhat difficult, to state exact relationships. However, it can be safely stated that the desired safety fuels are formulated from naphtha or gasoline fractions having minimum flash points less than 30 Fahrenheit degrees below the boiling point of the noninflammable organic addition agent, which must have a boiling point below the critical upper limit of 60 C. and be added in a concentration between 0.5% and 5% by volume, and preferably between about 1.0% and 2% by volume.

One of the distinguishing characteristics of the preferred noninflammable addition agents is that they contain only 1 to 2 carbon atoms in the molecule and contain one of the halogens other than chlorine, e. g. iodine, bromine, or fluorine. Also, as a rule, the polyhalides are more reliably less inflammable than the monohalides, and this fact is indicated more strikingly in the case of chlorine compounds; e. g., chloroform (CHC13) which is a border line noninflammable agent which can be used in the present invention, is satisfactorily noninflammable, but methyl chloride (CH3C1, B. pt.24 C.) and methylene chlo ride (CH2C12, B. pt. 40 C.) are not sufficiently noninflammable even though they have lower boiling points. Likewise, ethyl chloride and ethyl dichloride are not useful for the present purposes.

suitable for use as a carburant with an initiaf In a number of instances mixtures of the suitable noninflammable agents Work more satisfactorily, e. g. methyl iodide with methyl bromide, etc. but with the same limiting proportions for the combined agents.

It is to be understood that the specific examples which have been given are for the purposes of illustration and are not intended to limit the scope of the invention. There are variations which come within the spirit of the invention as defined in the following claims.

I claim:

1. The method of controlling the infiammability in motor fuels for high-compression sparkignition engines, which comprises blending from 0.5%to 5% by volume of a noninflammable organic halide boiling below the limit of about 60 C. F.) with a hydrocarbon fraction boiling substantially in the gasoline boiling range having an end boiling point below 437 F. and having a closed-cup flash point less than 30 Fahrenheit degrees below the boiling point of said organic halide to raise the closed cup flash point of the blend to above 124 F.

2. A method as described in claim 1, in which said organic halide is a bromide. v

3. A method as described in claim 1, in which said organic halide contains fluorine.

- 4. A method as described in claim 1, in which said organic halide is an iodide.

5. A safety aviation fuel for high-compression, spark-ignition engines, having a flash point above 124 F. and formulated by blending from 0.5% to 5% by volume of a noninflammable organic halide boiling below 60 C. with a hydrocarbon fuel boiling substantially within the gasoline boiling range having an end boiling point below 437 F. and having a flash point less than 30 Fahrenheit degrees below the boiling point of said organic halide.

6. A safety aviation motor fuel for high-compression spark-ignition engines with a closed-cup flash point substantially above 124 F., formulated by blending from 0.5% to 5% by volume of methyl iodide with a hydrocarbon fuel boiling substantially within the range of 280 F. to 425 F. and having a flash point of at least about 88 F., the proportion of methyl iodide being sufiicient to raise the flash point of the blend to above 124 F.

7. A safety aviation motor fuel for high-compression spark-ignition engines, formulated by blending from 0.5% to 5% by volume of methyl bromide with a hydrocarbon fuel fraction boiling substantially within the gasoline boiling range having an end boiling point below 437 F. and having a flash point of at least about 20 F. to raise the flash point of the blend to above 124 F.

8. A safety aviation motor fuel for high-compression spark ignition engines having a flash point above 124 F. and formulated by blending from 1% to 2% by volume of a noninflammable organic halide, containing only 1 to 2 carbon atoms per molecule and containing fluorine, with a hydrocarbon fuel boiling within the gasoline boiling range having an end boiling point below 437 F. and having a flash point less than 20 Fahrenheit degrees below the boiling point of said organic halide, the boiling point of said organic halide being essentially below C.

9. A fuel as described in claim 8, in which said organic halide is trichloro monofluoromethane.

10. A motor fuel having a flash point above 124 F. containing 0.5% to 5% by volume of a noninflammable organic halide having a boiling point below 60 C., and comprising a major proportion of a hydrocarbon liquid having an initial boiling point not lower than about F. and an end boiling point below 437 F. and a flash point not lower than 30 Fahrenheit degrees below the boiling point of said organic halide.

11. Motor fuel according to claim 10 in which the organic halide has only 1 to 2 carbon atoms and contains at least 4 halogen atoms.

12. Motor fuel according to claim 10 in which the organic halide contains a halogen having a difierent molecular weight than that of chlorine.

13. Motor fuel according to claim 10 in which the organic halide is a fluorinated derivative'of a hydrocarbon having only 1 to 2 carbon atoms.

14. Motor fuel according to claim 10 in which the organic halide contains only 1 to 2 carbon atoms and contains at least 3 fluorine atoms.

15. Motor fuel according to claim '10 in which the organic halide contains 1 to 2 carbon atoms and contains fluorine and another halogen.

16. Motor fuel according to claim lO in which the organic halide contains 1 to 2 carbon atoms and contains fluorine and chlorine.

WALTER A. HERBST. 

